Earth Atmosphere, on the Moon!

Terada et al. have demonstrated that oxygen from the Earth can be transported to the Moon’s surface. The core of their study reports the observation of high-speed (1-10 keV) oxygen ions, O+, by Japan’s Kaguya (SELENE) lunar orbiter. These high-speed O+ ions are only observed when 1) the Earth is between the Sun and the Moon, and 2) Kaguya is between the Earth and the Moon. This zone is where the Earth’s magnetic field excludes the Sun’s solar wind and channels the ions that have left the Earth. Terada et al. show that the composition of this terrestrial stream of oxygen is composed of 16O poor oxygen, similar to the isotopic weight of atmospheric ozone. It also matches a hitherto mysterious oxygen signature found in several lunar samples returned by the Apollo missions.

From Terada et al.:

A consequence of this finding is that the entire lunar surface can be contaminated with biogenic terrestrial oxygen, which has been produced by photosynthesis over a few billion years (with an estimate of 4×1036 O+ ions for about 2.4 billion years after the Great Oxygenation Event).

The implications are fascinating. Photosynthesis appears to have begun 2.4-2.7 billion years ago, and created the massive oxygen instability in our atmosphere (~20% O). Since that time, the Earth has been puffing this oxygen into nearby interplanetary space, where a good amount could get sucked up by the Moon’s surface. Over time, that sequestered oxygen would get buried by weathered lunar powder, thus creating an incredibly stable geologic (selenologic?) record of the Earth’s changing atmosphere. Whether that record could actually be teased out is debatable (and is questioned by Terada et al.), but perhaps deep core samples could provide a clear signal. In general, this work is another reminder that life on Earth has really been life in the Solar System. Sending people back to the Moon to study its rocks is a clearly indispensable step in understanding life’s interaction with both its home planet and its solar environment.

ABSTRACT

For five days of each lunar orbit, the Moon is shielded from solar wind bombardment by the Earth’s magnetosphere, which is filled with terrestrial ions. Although the possibility of the presence of terrestrial nitrogen and noble gases in lunar soil has been discussed based on their isotopic composition , complicated oxygen isotope fractionation in lunar metal (particularly the provenance of a 16O-poor component) re­mains an enigma . Here, we report observations from the Japanese spacecraft Kaguya of significant numbers of 1–10 keV O+ ions, seen only when the Moon was in the Earth’s plasma sheet. Considering the penetration depth into metal of O+ ions with such energy, and the 16O-poor mass-independent fractionation of the Earth’s upper atmosphere , we conclude that biogenic terrestrial oxygen has been transported to the Moon by the Earth wind (at least 2.6 × 104 ions cm−2 s−1) and implanted into the surface of the lunar regolith, at around tens of nanometres in depth. We suggest the possibility that the Earth’s atmosphere of billions of years ago may be preserved on the present-day lunar surface.

Biogenic oxygen from Earth transported to the Moon by a wind of magnetospheric ions
Kentaro Terada, Shoichiro Yokota, Yoshifumi Saito, Naritoshi Kitamura, Kazushi Asamura, Masaki N. Nishino
Nature Astronomy 1, Article number: 0026 (2017)

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